U.S. patent number 11,371,887 [Application Number 16/937,954] was granted by the patent office on 2022-06-28 for tunable coherent light filter for optical sensing and imaging.
This patent grant is currently assigned to BOARD OF REGENTS, THE UNIVERSITY OF TEXAS SYSTEM, U.S. DEPARTMENT OF ENERGY. The grantee listed for this patent is Board of Regents, The University of Texas System, National Technology & Engineering Solutions of Sandia, LLC. Invention is credited to Eric A. Shaner, Daniel Wasserman.
United States Patent |
11,371,887 |
Wasserman , et al. |
June 28, 2022 |
Tunable coherent light filter for optical sensing and imaging
Abstract
Systems and methods are provided for filtering coherent infrared
light from a thermal background for protection of infrared (IR)
imaging arrays and detection systems. A Michelson interferometer is
used for coherent light filtering. In an implementation, a system
includes a fixed mirror, a beam splitter, and a moving mirror which
can be controlled translationally, as well as tip/tilt. The
Michelson interferometer may be used as an imaging system. For
imaging applications, a system may comprise a tunable array of
micro-electromechanical systems (MEMS) mirrors. A mid-wave IR
interferometer with electronic feedback and MEMS mirror array is
provided.
Inventors: |
Wasserman; Daniel (West Lake
Hills, TX), Shaner; Eric A. (Albuquerque, NM) |
Applicant: |
Name |
City |
State |
Country |
Type |
Board of Regents, The University of Texas System
National Technology & Engineering Solutions of Sandia,
LLC |
Austin
Albuquerque |
TX
NM |
US
US |
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Assignee: |
BOARD OF REGENTS, THE UNIVERSITY OF
TEXAS SYSTEM (Austin, TX)
U.S. DEPARTMENT OF ENERGY (Washington, DC)
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Family
ID: |
1000006395778 |
Appl.
No.: |
16/937,954 |
Filed: |
July 24, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20210025760 A1 |
Jan 28, 2021 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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62878863 |
Jul 26, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01J
3/2803 (20130101); G01J 3/45 (20130101); G01J
5/06 (20130101); G01J 5/10 (20130101); G01J
3/021 (20130101); G01J 2003/2813 (20130101); G01J
2005/106 (20130101) |
Current International
Class: |
G01J
5/06 (20220101); G01J 3/02 (20060101); G01J
5/10 (20060101); G01J 3/28 (20060101); G01J
3/45 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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111896103 |
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Nov 2020 |
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CN |
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H11173921 |
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Jul 1999 |
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JP |
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2005505774 |
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Feb 2005 |
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JP |
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WO-2008101964 |
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Aug 2008 |
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WO |
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Other References
Coutinho, R. C., French, H. A., Selviah, D. R., Wickramasinghe, D.,
& Griffiths, H. D. (Nov. 1999). Detection of coherent light in
an incoherent background [for IRST]. In 1999 IEEE LEOS Annual
Meeting Conference Proceedings. LEOS'99. 12th Annual Meeting. IEEE
Lasers and Electro-Optics Society 1999 Annual Meeting (Cat. No.
99CH37009) (vol. 1, pp. 247-248). IEEE. cited by applicant .
Gruber Jr, Thomas, et al. "A small, low-cost, hyperspectral imaging
FTIR sensor design for standoff detection applications."
Next-Generation Spectroscopic Technologies V. vol. 8374.
International Society for Optics and Photonics, 2012. cited by
applicant.
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Primary Examiner: Taningco; Marcus H
Attorney, Agent or Firm: Meunier Carlin & Curfman
LLC
Government Interests
STATEMENT OF GOVERNMENT INTEREST
This invention was made with Government support under Contract No.
DE-NA0003525 awarded by the United States Department of
Energy/National Nuclear Security Administration. The Government has
certain rights in the invention.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of priority to U.S. Provisional
Patent Application No. 62/878,863, filed on Jul. 26, 2019, entitled
"TUNABLE COHERENT LIGHT FILTER FOR OPTICAL SENSING AND IMAGING,"
the contents of which are hereby incorporated by reference in their
entirety.
Claims
What is claimed:
1. A system comprising: an interferometer comprising: a beam
splitter configured to receive, from a light source, incident light
comprising at least coherent light, and split the light into a
split beam comprising two beams; two mirrors configured to each
receive a beam of the split beam and reflect the beam back to the
beam splitter for recombining into a recombined beam; and a
detector configured to receive the recombined beam; and a computing
device configured to determine an amount of the coherent light that
has been removed from the incident light, wherein the
interferometer is dynamically controlled via feedback from the
computing device to dynamically block coherent light of the light
source.
2. The system of claim 1, further comprising a translation stage
configured to translate at least one of the two mirrors to tune the
system to change the amount of the coherent light that is removed
from the incident light.
3. The system of claim 1, wherein the interferometer is a Michelson
interferometer, wherein the computing device is further configured
to measure the light transmitted through the interferometer to
determine the amount of the coherent light that has been removed
from the incident light.
4. They system of claim 1, wherein the interferometer is a mid-wave
IR interferometer.
5. The system of claim 1, further comprising the light source
configured to generate the incident light and transmit the incident
light to the beam splitter.
6. The system of claim 1, wherein the incident light has
wavelengths in the range from ultraviolet (UV) to visible to
terahertz (THz).
7. The system of claim 1, wherein the incident light further
comprises incoherent light.
8. The system of claim 1, wherein the incident light is in a
mid-infrared (mid-IR) wavelength range.
9. The system of claim 1, wherein the detector is an imaging
array.
10. The system of claim 1, wherein at least one of the mirrors is a
micro-electromechanical systems (MEMS) mirror array.
11. The system of claim 1, wherein the system is configured to
filter coherent infrared (IR) light from a thermal background for
protection of IR imaging arrays and detection systems.
12. A method for filtering coherent infrared light from a thermal
background for protection of infrared (IR) imaging arrays and
detection systems, the method comprising: receiving incident light,
from a light source, at a beam splitter of an interferometer;
splitting the incident light into a split beam; transmitting the
split beam down the length of two arms to two mirrors of the
interferometer; reflecting the split beam back to the beam
splitter; recombining the split beam into a recombined beam at the
beam splitter; transmitting the recombined beam to a detector of
the interferometer; determining, using a computing device, an
amount of coherent light that has been removed from the incident
light; and dynamically blocking coherent light of the light source
using the interferometer and feedback from the computing
device.
13. The method of claim 12, further comprising translating at least
one of the two mirrors to change the amount of the coherent light
that is removed from the incident light.
14. The method of claim 12, further comprising transmitting the
incident light to the beam splitter.
15. The method of claim 12, wherein the incident light has
wavelengths in the range from ultraviolet (UV) to visible to
terahertz (THz).
16. The method of claim 12, wherein the incident light comprises
coherent light and incoherent light.
17. The method of claim 12, wherein the incident light is in a
mid-infrared (mid-IR) wavelength range.
18. The method of claim 12, wherein the detector is an imaging
array.
19. The method of claim 12, wherein the mirror is a
micro-electromechanical systems (MEMS) mirror array.
20. The method of claim 12, wherein the beam splitter, the two
mirrors, and the detector are comprised within a Michelson
interferometer.
Description
BACKGROUND
The mid-infrared (mid-IR) wavelength range is of vital importance
for a range of sensing, security and defense, and fundamental
science applications. One of the primary applications for mid-IR
technologies is the use of infrared imagining arrays for thermal
imaging applications. For defense applications, these imagers are
used as night vision goggles, and as imagers on aircraft and
vehicles. Such imaging systems can be disabled by IR "jamming"
techniques, which typically involve the use of high powered lasers
to saturate or even destroy the pixels of the imaging system.
Thus, there is significant interest in developing techniques,
structures, or devices to protect these imaging arrays from such
attacks. One possible approach is the development of narrow band
notch filters, which are designed for a single wavelength, blocking
the design wavelength and passing all other wavelengths. Such
structures can be quite effective (using thin film interference or
more recently guided resonance mode filters). However, such filters
are not tunable, which means that for a jamming laser which is
capable of jumping around the spectrum, theses filters are not
suitable. It is expected that such tunable jamming lasers will be
deployed in the near future.
SUMMARY
An interferometric approach is provided for filtering coherent
infrared (IR) light from a thermal background for protection of IR
imaging arrays and detection systems. In an implementation, a
system includes a fixed mirror, a beam splitter, and a moving
mirror which can be controlled translationally, as well as
tip/tilt.
In some implementations, for imaging applications, a system may
comprise a tunable array of micro-electromechanical systems (MEMS)
mirrors.
In some implementations, a mid-wave IR interferometer with
electronic feedback and MEMS mirror array is provided.
This summary is provided to introduce a selection of concepts in a
simplified form that are further described below in the detailed
description. This summary is not intended to identify key features
or essential features of the claimed subject matter, nor is it
intended to be used to limit the scope of the claimed subject
matter.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary, as well as the following detailed
description of illustrative embodiments, is better understood when
read in conjunction with the appended drawings. For the purpose of
illustrating the embodiments, there is shown in the drawings
example constructions of the embodiments; however, the embodiments
are not limited to the specific methods and instrumentalities
disclosed. In the drawings:
FIG. 1 is a diagram of an exemplary system for tunable coherent
light filtering;
FIG. 2 is an illustration of an exemplary interferogram showing
coherent behavior;
FIG. 3 is an illustration of an exemplary interferogram showing
incoherent behavior;
FIG. 4 is an illustration of an exemplary interferogram showing
combined coherent behavior and incoherent behavior;
FIG. 5 is an illustration of an exemplary system for performing and
testing for tunable coherent light filtering;
FIG. 6 is an illustration of an exemplary scan showing test
results;
FIG. 7 is an illustration of a stand-alone interferometer with a
3.39 .mu.m HeNe laser source;
FIG. 8 is an illustration of a plot of the signal through the
interferometer of FIG. 7 as function of mirror position;
FIG. 9 is an operational flow of an implementation of a method for
tunable coherent light filtering; and
FIG. 10 shows an exemplary computing environment in which example
embodiments and aspects may be implemented.
DETAILED DESCRIPTION
FIG. 1 is a diagram of an exemplary system 100 for tunable coherent
light filtering. In the system 100, a Michelson interferometer 105
is in communication with a computing device 190. In some
implementations, the Michelson interferometer 105 and the computing
device 190 may be in communication with each other through a
network, or in direct communication without a network connection.
In other implementations, the computing device 190 may be
integrated into the Michelson interferometer 105, e.g., in a
programmable field programmable gate array (FPGA) type system. A
suitable computing device is illustrated in FIG. 10 as the
computing device 1000. Although only Michelson interferometer 105
and one computing device 190 are shown in FIG. 1, there is no limit
to the number of Michelson interferometers 105 and computing
devices 190 that may be supported.
As described further herein, the computing device 190 may measure a
signal from a detector 160 as a function of a position of one or
more of the mirrors 140, 150.
The Michelson interferometer 105 (alone in some implementations,
and in conjunction with the computing device 190 in other
implementations) provide the ability to filter coherent IR signals,
which is of vital importance for protecting IR imaging arrays. As
described further herein, the Michelson interferometer 105 is used
for coherent light filtering. In some implementations, the
Michelson interferometer 105 may be used as an imaging system (as
opposed to simply integrating the intensity of the transmitted
signal).
The disclosed invention takes a different approach to filtering a
jamming signal (i.e., the incident light (e.g., from a light
source, such as the laser 110)), focusing on the coherent nature of
the jamming signal, as opposed to its spectral signature.
The Michelson interferometer 105 comprises a translation stage 120
which may be used to adjust one or more of the two reflecting
mirrors 140, 150 (e.g., translationally, as well as tip/tilt), a
beam splitter 130, and a detector 160. In an implementation, one of
the reflecting mirrors (e.g., the mirror 140) is fixed, and the
other mirror (e.g., the mirror 150) is mobile (can be moved
translationally, tilted, and/or tipped). A light source 110, such
as a laser, is shown in FIG. 1, along with a thermal source 112.
The light source 110 and the thermal source 112 are external to the
Michelson interferometer 105.
The beam splitter 130 splits the incident light from the light
source 110 into two arms terminated by the mirrors 140, 150,
respectively. The split beam travels the length of the two arms and
then returns to the beam splitter 130, where it is recombined and
then travels on to the detector 160.
In some implementations, the detector 160 comprises an imaging
array, such as an infrared focal plane array (FPA) or a charge
coupled device (CCD) detector. In some implementations, the moving
mirror (e.g., the minor 150) comprises a mirror array, such as a
micro-electromechanical systems (MEMS) minor array.
If the arm lengths are equal (so-called zero path difference or
ZPD), then the light recombines constructively and the full signal
is detected at the image plane of the detector 160. If, however,
the two arms have a length difference of .DELTA.d (total path
length difference of 2.DELTA.d), then light having wavelength
.lamda.=4.DELTA.d will interfere destructively and will not be
detected at the image plane of the detector 160.
Thus, as the translation stage 120 is adjusted (e.g., manually,
responsive to feedback, by instructions received from the computing
device 190, etc.) so that the moving arm pertaining to the mirror
150 is translated, one would expect to see a series of constructive
and destructive interference peaks and valleys. The intensity vs.
path length plot is known as an interferogram, and taking the
Fourier transform of an interferogram gives the spectrum of the
incident light (the basis of the Fourier transform infrared (FTIR)
spectrometer). However, this analysis, in addition to assuming the
light is monochromatic, assumes the light is perfectly coherent,
such that infinitely long path differences still result in
interference. This is a reasonable assumption for a laser, but not,
it turns out, for incoherent light. Incoherent light will show
interference fringes near the ZPD position, but the amplitude of
these fringes will quickly die out as path length difference
increases. At lengths greater than the coherence length of the
light, one basically sees no more interference, with one-half of
the light transmitted to the detector 160, and the other one-half
of the light reflected back to the light source 110.
Thus, in accordance with implementations, the Michelson
interferometer 105 can be positioned such that the path length
difference is greater than the coherence length, and can pass 50%
of the incoherent light, and depending on the fine position of the
minor, can either block or pass .about.100% of the coherent signal.
Moreover, slight changes in the mirror position of the mirror 150
allows for the filtering (blocking) of coherent signals across a
broad range of IR wavelengths. Although embodiments and examples
herein are directed to light have IR wavelengths, the invention is
not limited to these wavelengths, and other wavelengths of light
are contemplated, such as light having wavelengths in the range
from ultraviolet (UV) to visible to terahertz (THz), for
example.
In an embodiment, the Michelson interferometer 105 operates away
from ZPD, through which one can image, and is dynamically
controlled via electronic feedback mechanisms of the computing
device 190, in order to block any monochromatic coherent signal of
the light source 110. In addition, a dynamic pixelated minor may be
used as one or both of the minors 140, 150 to individually minimize
coherent light transmission by control of MEMS micromirrors. In
this manner, a MEMS minor array may be provided with electronic
feedback for high speed dynamic filtering of coherent light.
The translation stage 120 may be stepped through to adjust the
movable minor 150 position to find where the coherent light
destructively interferes. Whenever the minor is not close to the
position of ZPD, incoherent light interferes very little, but
coherent light exhibits minima and maxima.
FIG. 2 is an illustration of an exemplary interferogram 200 showing
coherent behavior (i.e., interferogram of coherent light). FIG. 3
is an illustration of an exemplary interferogram 300 showing
incoherent behavior (i.e., interferogram of incoherent light). As
shown in the interferograms 200, 300, respectively, the coherent
light has many maximums of similar height, while the incoherent
light only forms one large maximum.
FIG. 4 is an illustration of an exemplary interferogram 400 showing
combined coherent behavior and incoherent behavior. The
interferogram 400 shows that if the mirror is held away from ZPD,
it can be fine adjusted to sit a signal maximum (e.g., 50% of the
incoherent light and nearly 100% of the coherent light reaching the
detector 160) or at a minimum (e.g., 50% of the incoherent light
and nearly 0% of the coherent light reaching the detector 160).
FIG. 5 is an illustration of an exemplary system 500 for performing
and testing for tunable coherent light filtering. The system
comprises two Michelson interferometers 505, 570. The Michelson
interferometer 505 comprises a translation stage 520 which may be
used to adjust one or more of the two reflecting mirrors 540, 550
(shown as gold minors), and a beam splitter 530. In an
implementation, one of the reflecting minors (e.g., the mirror 540)
is fixed, and the other minor (e.g., the mirror 550) is mobile.
Coherent light, which ultimately is to be filtered, is generated by
a light source 510, which in an implementation comprises a CO.sub.2
laser.
The Michelson interferometer 505 is similar to the Michelson
interferometer 105 but does not have a detector such as the
detector 160. Instead, the system 500 comprises an aperture 560
through which the recombined light beam passes to a
Fourier-transform infrared spectroscopy (FTIR) spectrometer 590. In
implementation, the FTIR spectrometer 590 is a VERTEX 70v FTIR
spectrometer. The FTIR spectrometer 590 comprises the Michelson
interferometer 570 and an MCT (mercury cadmium telluride or HgCdTe)
detector 580.
The Michelson interferometer 505 is placed outside the FTIR
spectrometer 590 and is used to minimize the coherent light before
scanning the recombined light beam with the FTIR spectrometer 590.
Thus, the Michelson interferometer 505 filters the coherent light
before it reaches the FTIR spectrometer 590. The remaining signal
(the recombined light beam) can then be scanned to determine what
proportion of the original light is filtered. The invention is thus
integrated into an emission spectroscopy scheme to show that it can
filter coherent light from incoherent light. A computing device 190
may be implemented to receive, store, and/or display or otherwise
output results from the FTIR spectrometer 190.
FIG. 6 is an illustration of an exemplary scan 600 showing test
results. The scan 600 shows an extinction ratio of about 90/12, or
-8.75 dB. Better alignment of the interferometers will improve the
extinction ratio.
FIG. 7 is an illustration of a stand-alone interferometer 700. The
interferometer 700 is a home-built interferometer with a 3.39 .mu.m
HeNe laser source.
FIG. 8 is an illustration of a plot 800 of the signal through the
interferometer 700 of FIG. 7 as function of mirror position. The
plot 800 demonstrates .about.97% attenuation from peak transmission
when the mirror is positioned at an interference null. Thus, when
the mirror position is scanned, there is an extinction of the
signal of about 97%.
FIG. 9 is an operational flow of an implementation of a method 900
for tunable coherent light filtering. The method 900 may be
implemented using the system 100.
At 910, incident light (which may be generated by a light source
such as the laser 110) is received at a beam splitter, such as the
beam splitter 130. The incident light may comprise coherent light
and/or incoherent light.
At 920, the light is split into two beams by the beam splitter 130.
At 930, the split beam travels the arms to the mirrors (e.g., the
mirrors 140, 150) and reflected by the mirrors and returned to the
beam splitter 130. At 940, the split beam is recombined at the beam
splitter 730.
At 950, the recombined split beam is transmitted to a detector,
such as the detector 160. At 960, the amount (e.g., percentage) of
coherent light that has been removed may be determined, e.g., by
the computing device 190. At 970, one or more of the mirrors may be
adjusted (e.g., using a translation stage such as the translation
stage 120) to tune or change the amount of coherent light to be
removed (i.e., filtered).
It is noted that advantages and benefits of the embodiments
described herein include: tunable filtering; the ability to
differentiate between coherent and incoherent light; strong
quenching of a coherent signal (e.g., depending on the optics,
there may be a .about.99% rejection of the coherent signal);
broadband transmission of an incoherent signal; polarization
insensitive; broadband (covers 3 .mu.m-5 .mu.m range or other
infrared, UV, visible, or THz bands); and fast tuning.
It is contemplated that aspects of the invention may also be used
to filter out a coherent pump laser in resonant excitation
fluorescence spectroscopy.
FIG. 10 shows an exemplary computing environment in which example
embodiments and aspects may be implemented. The computing device
environment is only one example of a suitable computing environment
and is not intended to suggest any limitation as to the scope of
use or functionality.
Numerous other general purpose or special purpose computing devices
environments or configurations may be used. Examples of well-known
computing devices, environments, and/or configurations that may be
suitable for use include, but are not limited to, personal
computers, server computers, handheld or laptop devices,
multiprocessor systems, microprocessor-based systems, network
personal computers (PCs), minicomputers, mainframe computers,
embedded systems, distributed computing environments that include
any of the above systems or devices, and the like.
Computer-executable instructions, such as program modules, being
executed by a computer may be used. Generally, program modules
include routines, programs, objects, components, data structures,
etc. that perform particular tasks or implement particular abstract
data types. Distributed computing environments may be used where
tasks are performed by remote processing devices that are linked
through a communications network or other data transmission medium.
In a distributed computing environment, program modules and other
data may be located in both local and remote computer storage media
including memory storage devices.
With reference to FIG. 10, an exemplary system for implementing
aspects described herein includes a computing device, such as
computing device 1000. In its most basic configuration, computing
device 1000 typically includes at least one processing unit 1002
and memory 1004. Depending on the exact configuration and type of
computing device, memory 1004 may be volatile (such as random
access memory (RAM)), non-volatile (such as read-only memory (ROM),
flash memory, etc.), or some combination of the two. This most
basic configuration is illustrated in FIG. 10 by dashed line
1006.
Computing device 1000 may have additional features/functionality.
For example, computing device 1000 may include additional storage
(removable and/or non-removable) including, but not limited to,
magnetic or optical disks or tape. Such additional storage is
illustrated in FIG. 10 by removable storage 1008 and non-removable
storage 1010.
Computing device 1000 typically includes a variety of computer
readable media. Computer readable media can be any available media
that can be accessed by the device 1000 and includes both volatile
and non-volatile media, removable and non-removable media.
Computer storage media include volatile and non-volatile, and
removable and non-removable media implemented in any method or
technology for storage of information such as computer readable
instructions, data structures, program modules or other data.
Memory 1004, removable storage 1008, and non-removable storage 1010
are all examples of computer storage media. Computer storage media
include, but are not limited to, RAM, ROM, electrically erasable
program read-only memory (EEPROM), flash memory or other memory
technology, CD-ROM, digital versatile disks (DVD) or other optical
storage, magnetic cassettes, magnetic tape, magnetic disk storage
or other magnetic storage devices, or any other medium which can be
used to store the desired information and which can be accessed by
computing device 1000. Any such computer storage media may be part
of computing device 1000.
Computing device 1000 may contain communication connection(s) 1012
that allow the device to communicate with other devices. Computing
device 1000 may also have input device(s) 1014 such as a keyboard,
mouse, pen, voice input device, touch input device, etc. Output
device(s) 1016 such as a display, speakers, printer, etc. may also
be included. All these devices are well known in the art and need
not be discussed at length here.
It should be understood that the various techniques described
herein may be implemented in connection with hardware components or
software components or, where appropriate, with a combination of
both. Illustrative types of hardware components that can be used
include Field-programmable Gate Arrays (FPGAs),
Application-specific Integrated Circuits (ASICs),
Application-specific Standard Products (ASSPs), System-on-a-chip
systems (SOCs), Complex Programmable Logic Devices (CPLDs), etc.
The methods and apparatus of the presently disclosed subject
matter, or certain aspects or portions thereof, may take the form
of program code (i.e., instructions) embodied in tangible media,
such as floppy diskettes, CD-ROMs, hard drives, or any other
machine-readable storage medium where, when the program code is
loaded into and executed by a machine, such as a computer, the
machine becomes an apparatus for practicing the presently disclosed
subject matter.
Although exemplary implementations may refer to utilizing aspects
of the presently disclosed subject matter in the context of one or
more stand-alone computer systems, the subject matter is not so
limited, but rather may be implemented in connection with any
computing environment, such as a network or distributed computing
environment. Still further, aspects of the presently disclosed
subject matter may be implemented in or across a plurality of
processing chips or devices, and storage may similarly be effected
across a plurality of devices. Such devices might include personal
computers, network servers, and handheld devices, for example.
Although the subject matter has been described in language specific
to structural features and/or methodological acts, it is to be
understood that the subject matter defined in the appended claims
is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are disclosed as example forms of implementing the
claims.
* * * * *